1. Field of the Invention
The present invention relates to a semiconductor device provided with a function to control by a transistor a current supplied to a load. More particularly, the invention relates to a display device including a pixel formed of a current drive type light emitting element of which luminance changes according to a current, a signal line driver circuit thereof, and a driving method thereof. Further, the invention relates to an electronic device including the display device in a display portion.
2. Description of the Related Art
In recent years, so-called a self-luminous type display device of which pixels are formed of light emitting elements such as light emitting diodes (LEDs) is attracting attention. As a light emitting element used for such a self-luminous type display device, an organic light emitting diode (OLED), an organic EL element, and an electroluminescence (EL) element are attracting attention and becoming to be used for an organic EL display and the like.
A light emitting element such as an OLED which emits light by itself is advantageous in that visibility of pixels is higher as compared to a liquid crystal display, a backlight is not required, and response is fast. The luminance of a light emitting element is controlled by a current value supplied to the light emitting element. Therefore, a constant current drive in which a constant amount of current is supplied to the light emitting element is suggested for accurately displaying gray scales (see Patent Document 1).    [Patent Document 1]    Japanese Patent Laid-Open No. 2003-323159
A light emitting element has a property that resistance (internal resistance) changes in accordance with the temperature. In specific, when the temperature becomes higher than the normal temperature, the resistance decreases while the resistance increases when the temperature becomes lower than the normal temperature. Accordingly, when the temperature rises, a luminance higher than desired is obtained as a current value increases and the current value decreases when the temperature falls, even though a constant voltage is applied by a constant voltage drive.
Due to the aforementioned properties of a light emitting element, luminance thereof varies when the temperature changes. In view of the aforementioned, the invention provides a display device which suppresses the influence of luminance variations of a light emitting element due to a temperature change.